1. Field of the Invention
The present invention relates generally to the art of earth boring and, more particularly, to rotary rock bits having a sealed lubrication system.
2. Description of the Prior Art
A rotary rock bit generally consists of a main bit body adapted to be connected to a rotary drill string. A conventional bit usually includes two or more legs integrally connected to form a bit body. Each leg includes a cutter rotatively mounted on a journal pin extending from the leg. Bearing assemblies are provided between the cutter and the journal pin to promote rotation of the cutter. Either milled teeth, tungsten carbide inserts or the like are provided on the outer surface of the cutter for disintegrating the formations as the bit and cutter rotate.
A sufficient supply of lubricant is provided to the bearing assemblies by means of a reservoir having passageways communicating with the bearing assemblies. A seal such as an O-ring seal is positioned within a gland between each cutter and leg to prevent lubricant from leaking to the exterior of the bit and prevent drilling fluid and other matter from entering into the bearing area. Such a lubrication system is shown in U.S. Pat. Nos. 3,917,028 and 4,061,376.
A problem encountered with seal bearing bits is that in certain drilling environments such as drilling through shale, the shale would work its way across the sealing face of the O-ring seal to attack the O-ring seal and cause undue wear thereon. This shale packing further acts on the seal assembly to effectively increase the squeeze on the O-ring seal thereby shortening its life because of increased friction.
Another problem encountered with sealed bearing bits is that O-ring seals tend to move axially within the gland due to the internal and external pressure differential while drilling. This movement is a wave-type movement (sometimes called Marcelling) which is detrimental to the seal because, during such movement, the O-ring seal has a tendency to bunch or wrap up.
Still another problem with sealed bearing bits is that in any environment the friction on the outer diameter of the O-ring seal is excessive and creates undue wear thereon.